MicroRNAs (miRNAs) are endogenous RNAs, some of which are known to regulate the expression of protein-coding genes at the posttranscriptional level. During miRNA maturation in animals, the primary transcript is first processed to a stem-loop precursor and then the stem-loop is processed to yield a mature miRNA of about 22-nucleotides. These molecules can direct the cleavage of mRNA or they can interfere with productive translation of the mRNA, either of which results in reduced protein accumulation and hence the miRNAs are able to modulate gene expression and related cellular activities. miRNAs are important in development and differentiation, and thus the altered expression of miRNAs could be used to alter development and differentiation during tissue engineering and other applications. Furthermore, miRNA-like stem-loops can be expressed in cells as a vehicle to deliver artificial miRNAs and short interfering RNAs (siRNAs) for the purpose of modulating the expression of endogenous genes through the miRNA and or RNAi pathways. This can be a useful tool for studying gene function, human therapies, and other applications. However, current methods for expressing miRNAs, artificial miRNAs, and siRNAs are inefficient and are not effective for many small RNA sequences.